1. Technical Field
The present invention relates to an active matrix substrate, a method for manufacturing it, an electro-optical device, and an electronic apparatus.
2. Related Art
Along with the popularization of mobile apparatuses such as notebook personal computers and cellular phones, thin-and-light liquid display devices are widely used. A liquid crystal display has a structure in which a liquid crystal layer is sandwiched between an upper substrate and a lower substrate.
An example of the lower substrate (active matrix substrate) is shown in FIG. 21. As shown in FIG. 21, a lower substrate 1 is provided with a glass substrate 2, a gate scanning electrode 3 and a source electrode 4 both of which are wired so as to intersect each other on the glass substrate 2, a drain electrode 5 wired on the glass substrate 2, a pixel electrode 6 (ITO) connected to the drain electrode 5, an insulation layer 7 interposed between the gate scanning electrode 3 and the source electrode 4, and a thin film transistor (TFT) 8 made of a thin film semiconductor.
For forming metal wiring lines in the lower substrate 1, a method is used as exemplified in Japanese Patent No. 3261699. In the method, a process combining dry processing and photolithographic etching is repeated several times.
The method, however, has a problem in that material costs and administrative costs increase, while a yield rate is hardly increased since the process combining dry processing and photolithographic etching is carried out several times.
Thus, in recent years, a use of liquid discharge methods has been increased as a coating method used in manufacturing processes of electronic apparatuses. In a coating technique by means of liquid discharge methods, generally, liquids are discharged as droplets from a plurality of nozzles provided to a liquid discharge head while a substrate and the liquid discharge head are relatively moved so that the droplets are repeatedly deposited on the substrate to form a coated film. Therefore, this method consumes liquid with less waste and any patterns can directly be coated without using means such as photolithography.
For example, a technique is disclosed in JP-A-11-274671 and JP-A-2000-216330, in which a fine wiring pattern such as for a semiconductor integrated circuit is formed by discharging a functional liquid containing a pattern forming material onto a substrate from a liquid drop discharge head so as to provide or coat the material onto a pattern forming surface.
In addition, a method is disclosed in JP-A-2005-012181 in which, when a gate electrode having a width narrower than a gate wiring line is formed, a droplet containing a conductive material is coated to a gate wiring line groove. Liquids formed by the droplet autonomously flow in the gate electrode groove by a capillary phenomenon, thereby being disposed in the groove.
However, the above-mentioned related art technique has the following setbacks.
Characteristics of a TFT element formed on a gate electrode depend on flatness of amorphous silicon. The flatness of amorphous silicon is influenced by flatness of the gate electrode.
Therefore, particularly when a gate electrode is formed by the above-mentioned droplet discharge method, a problem arises in that flatness is lowered due to a rough surface caused by large-size grains of fine particles that are fusion bonded by a heat in firing when a droplet containing silver fine particles is used, for example.